Dehairing of hides and skins

ABSTRACT

A METHOD OF DEHAIRING SKINS AND HIDES CONSISTING OF TREATING THE SKINS AND HIDES WITH AN AQUEOUS SOLUTION CONTAINING AN INORGANIC PER COMPOUND AND AN INORGANIC BASE AT A PH OF ABOUT 10 TO 13.5 UNTIL THE HAIR IS SUFFICIENTLY LOOSENED TO PERMIT ITS MECHANICAL REMOVAL FROM THE SKINS AND HIDES.

United States Patent 3,574,516 DEHAIRING 0F HIDES AND SKINS Eckhart Heidemann, Darmstadt, and Fritz Hahn, Frankfurt am Main, Germany, assignors to Deutsche Goldund Silber-Scheideanstalt vormals Roessler No Drawing. Filed Mar. 28, 1966, Ser. No. 537,671 Int. Cl. C14c 1/06 US. Cl. 8-94.16 7 Claims ABSTRACT OF THE DISCLOSURE A method of dehairing skins and hides consisting of treating the skins and hides with an aqueous solution containing an inorganic per compound and an inorganic base at a pH of about 10 to 13.5 until the hair is sufficiently loosened to permit its mechanical removal from the skins and hides.

The present invention relates to a process for dehairing skins and hides, as well as a composition for carrying out such process based on compound having an oxidizing action which not only preserves the skins and hides but also permits recovery of the hair in view of its preservation during the dehairing and in addition avoids poisonous waste water.

Recently acid solutions of sodium chlorite have been suggested for dehairing hides and skins. Chlorous acid and C10 are produced in such solutions. The dehairing with such solutions proceeds in such a manner that the hair was always destroyed starting from the hair tip so that the decomposition products thereof are present in the waste water as they are dissolved to such an extent that they cannot be filtered off. The resulting albumen content in the waste water cannot at the present time be toler ated by the industry and can only be decreased with great difiiculty. In addition, the industry has found that the oxidative attack on the collagen of the dehaired hide resulting from the process is a substantial disadvantage as it engenders a considerable reduction in tear strength of leathers produced therefrom.

The object of the invention is to provide a process and composition for use therein for dehairing hides based on compounds having an oxidizing action which avoids the aforementioned disadvantages and in addition renders it possible to recover the hair removed in the dehairing operation in such a form that they may be used for other purposes.

The essence of the invention resides in that the skins and hides to be dehaired are treated with an aqueous solution of peroxides or active oxygen yielding compounds at a pH between 10 and 13.5 in the presence of an inorganic base and, if desired, in the presence of an organic base and/or of a neutral salt. Examples of suitable oxidizing agents, for instance, are peroxides, such as, sodium peroxide and hydrogen peroxide, as well as sodium perborate. The quantity of oxidizing agent employed preferably is between about 0.5 and 5% based upon the weight of the skins or hides treated. Alkali metal or alkaline earth metal hydroxides can, for example, 'be used as the inorganic base. Preferably, the quantity of the inorganic base is between about 0.5 and 5% and that of the organic base, such as a lower alkyl amine of l-S carbon atoms is between about 0.5 and 3% based upon the weight of the skins treated. The water soluble alkali metal or alkaline earth metal halides or sulfates can, for example, be employed as the added neutral salts. Preferably, the quantity of the neutral salts employed is between 1.0 and 5.0% based on the weight of the skins treated.

In the process according to the invention, the hair is loosened at the root, as in dehairing with alkali metal or alkaline earth metal sulfides, and can be removed easily.

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The hair itself undergoes very little attack. A bleaching effect is achieved on the hair which is of advantage in the further processing of the hair. The essential advantage of the process according to the invention therefore is that the hair is preserved as it is not dissolved during the dehairing operation and can be recovered if it already is separated from the skins in the treating drum, simply by filtration of the liquor or if this is not the case with the usual machines used in the tannery. In addition, the process according to the invention renders it possible to avoid the presence of sulfur ions which represent a strong poison in waste water and which cannot be avoided in most dehairing procedures which have been introduced commercially.

A further advantage of the process according to the invention is that in addition to the hair the dehaired hides also are bleached. After tanning of the pure white dehaired skins obtained it is possible to effect a very uniform aniline dyeing. At present all means are sought after which can increase the portion of the skins which can be processed to aniline dyed leather.

In comparison with the prior processes, only short times are required to effect loosening of the hair whereby loss of skin substance with reduction of tearing strength and other consequences engendered thereby are reduced substantially or avoided.

Aqueous solutions of sodium peroxide containing calcium hydroxide as well as an amine, such as, dimethyl amine or a neutral salt, such as, calcium chloride have proved particularly suited for the purposes of the invention.

The following examples will serve to illustrate the invention with reference to several embodiments thereof.

EXAMPLE 1 EXAMPLE 2 1000 kg. of softened cow hides were treated with 20 kg. of Na O dissolved in 1000 kg. of water and 40 kg. of calcium hydroxide as well as 5 kg. of calcium chloride in a dehairing drum with occasional movement as described in Example 1. The time required for the treatment was up to a maximum of 50% longer than that required in EX- ample 1 but the swelling as compared to that of Example 1 was reduced.

EXAMPLE 3 1000 kg. of softened cow hides were treated with 15- 17.5 kg. of Na O dissolved in 1000 kg. of water and 30 kg. of calcium hydroxide as well as 2.5 to 5 kg. of a 30% dimethyl amine solution in a dehairing drum with occasional movement as described in Example 1. The swelling as compared to that of Example 1 was significantly reduced and the loosening of the hair substantially improved over that of Example 2.

EXAMPLE 4 1000 kg. of softened calf skins were treated on the flesh side with a solution prepared by dissolving or suspending 2025 kg. of Na 0 40 kg. of calcium hydroxide and 5 kg. of a 30% dimethyl amine solution in kg. of water. After 16 hours the hair which was hardly attacked was removed mechanically. The skins were only slightly swollen.

3 EXAMPLE 5 1000 kg. of softened calf skins were treated with kg. of Na O dissolved in 1000 kg. of water, 30 kg. of calcium hydroxide and 5 kg. of a 30% dimethyl amine solution in a drum with only occasional slow movement of the drum. After 24 hours treatment, the hair was removed with a dehairing machine.

EXAMPLE 6 1000 kg. of softened calf skins were treated with 25- kg. of Na O dissolved in 1000 kg. of water, 50 kg. of calcium hydroxide and 5 kg. of calcium chloride in a drum with only occasional slow movement of the drum as in Example 5. While the swelling was significantly reduced over that of Example 5, the loosening of the hair was sufiicient that it could easily be removed mechanically.

EXAMPLE 7 1000 kg. of softened calf skins were treated with 25 kg. of Na O dissolved in 5000-10,000 kg. of water, 50 kg. of calcium hydroxide and 5 kg. of a 30% dimethyl amine solution as described in Example 5. This embodiment of the process permits an optimal protection of the skins against mechanical influences.

EXAMPLE 8 100 kg. of softened and defleshed cow hides were treated with a solution of 2-3 kg. of NaOH, 2-4 kg. of H 0 by weight) and 2-5 kg. of sodium sulfate in 50 to 200 kg. of water in a drum. The hair was completely removed after 10-15 hours treatment.

EXAMPLE 9 ganic per compound selected from the group consiting of sodium peroxide, sodium perborate and hydrogen peroxide in an amount of 0.5 to 5% based upon the weight of the skins and hides and containing an inorganic base selected from the group consiting of alkali metal and alkaline earth metal hydroxides of a pH of about 10 to 13.5 until the hair is sufiiciently loosened to permit its mechanical removal from the skins and hides.

2. The method of claim 1 in which the quantity of said inorganic base is 0.5 to 5% based upon the weight of the skins and hides.

3. The method of claim 2 in which said aqueous solution also contains 0.5 to 3% of a lower slkyl amine of 1-5 carbon atoms based upon the weight of the skins and hides.

4. The process of claim 3 in which said lower alkyl amine is dimethyl amine.

5. The process of claim 4 in which said per compound is sodium peroxide.

6. The method of claim 2 in which said aqueous solution also contains 1 to 5% of a salt selected from the group consisting of neutral water soluble alkali metal and alkaline earth metal sulfates and chlorides.

7. The method of claim 6 in which said salt is calcium chloride.

References Cited UNITED STATES PATENTS 2,353,878 8/1944 Christopher 894.16

FOREIGN PATENTS 451,115 1935 Great Britain 8--111X 1,362,720 1964 France 8-94.16X

OTHER REFERENCES Wool-Its Chemistry and Physics, Alexander and Hudson, 1954, pp. 260-64.

LEON D. ROSDOL, Primary Examiner M. HALPERN, Assistant Examiner U.S. Cl. X.R. 8-94.15

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3.574 .516 Dated April 13, 1971 lnventofls) Eckhart Heidemann et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, after line insert Claims priority, application Germany, March 26, 196

Signed and sealed this 23rd day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

